Method of making alkyl esters using glycerin

ABSTRACT

A method for making alkyl esters (e.g., methyl ester), such as biodiesel, from an oil source is described. The method involves converting the free fatty acids of the oil source into a mixture of mono-, di-, and tri-glycerides and subsequently transesterifying the newly formed glycerides as well as the originally present glycerides into fatty acid alkyl esters.

RELATED APPLICATIONS

This is a continuation-in-part of U.S. application Ser. No. 10/639,048, filed on Aug. 12, 2003 now U.S. Pat. No. 6,822,105. The 10/639,048 application is hereby incorporated by reference herein for purposes of continuity of disclosure and the like.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

BACKGROUND OF THE INVENTION

Alkylesters, or methylester specifically, such as biodiesel, are a clean-buming replacement for conventional petroleum-based diesel. Biodiesel may be made from natural, renewable sources such as new or used vegetable oils and animal fats. Biodiesel is fatty acid alkyl esters (typically being C₁₆ to C₁₈) and can generally be burned in combustion-ignition engines as a direct replacement for petroleum-based diesel. Aside from providing the benefit that biodiesel may be generated from renewable sources, biodiesel also provides the added benefit of decreased emissions from its combustion as compared to the combustion of petroleum-based diesel.

Alkylesters, in particular biodiesel, may be derived from the oils of the soybean or the rapeseed. The crude vegetable oil from these sources may be filtered, refined and subjected to several processing steps before the oil may be usable as biodiesel. Additionally, biodiesel may be derived from varying grades of vegetable oils. Such grades include virgin oil, yellow grease, used oils from food processing, or by-products from the edible oil refining process such as soap stock. Each of these sources has varying amounts of free fatty acids and/or glycerides—i.e., mono-, di-, or tri-glycerides—that may be processed into biodiesel.

Of these sources of vegetable oil, soap stock is generally considered the most cost effective source. Soap stock is derived from the crude oil extracted from the soybean or rapeseed. The crude oil of these seeds may be separated into two components: refined oil (which may then be further processed and converted into edible oil) and soap stock. The soap stock may then be acidulated with sulfuric acid to provide a composition having about 70% free fatty acids that may be further processed into biodiesel.

One contemplated method of processing the free fatty acids from these various grades of vegetable oils is the direct transesterification of the free fatty acids in the presence of alkali to produce the fatty acid alkyl esters for use as biodiesel. Such an approach, however, causes the free fatty acids to precipitate as soap, creating an additional recovery step in the contemplated method.

To avoid the precipitation problem, a two-step method for processing the free fatty acids has been proposed. This method can be found in EP 07 708 813 and WO 02/28811, and generally consists of the steps of (1) acid catalyzed esterification of free fatty acids with methanol in the presence of sulfuric acid, and (2) neutralization of the acid catalyst followed by conventional base catalyzed transesterification. These steps can be described by the following reaction scheme.

where each R may be the same or different and an aliphatic chain typically found in vegetable or animal oil sources, typically C₈ to C₂₂.

Even though transesterifications are both acid and base catalyzed, neutralization of the acid catalyst is necessary because acid catalyzed transesterifications typically exhibit slower kinetics than base catalyzed transesterifications, under comparable conditions. The disadvantages of two-step methods as disclosed in EP 07 708 813 and WO 02/28811 are the additional salt waste from neutralization, long cycle times, and a cumbersome recovery scheme of residual free fatty acids, as well as the need to separate methanol from water for recovery and/or waste disposal reasons.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method of processing free fatty acids from a vegetable or animal oil source into alkylesters in which the salt and aqueous waste is reduced or eliminated.

It is a further object of the present invention to provide a method of processing free fatty acids from a vegetable or animal oil source into alkylesters in which the necessity to separate alkylalcohol (e.g. methanol) from reaction water is reduced or eliminated.

It is a further object of the present invention to provide a method of processing free fatty acids from a vegetable or animal oil source into alkylesters, particularly biodiesel, in which the recovery scheme of residual free fatty acids is conveniently performed or the need for such recovery is eliminated.

These and other advantages are accomplished by subjecting the vegetable or animal oil source to a glycerin source first to convert the free fatty acid content of the oil source into glycerides and in a second step convert the newly created glycerides as well as the originally present glycerides into fatty acid alkyl esters for use as biodiesel. The two-step process of the present invention does not involve a neutralization step or the separation of alcohol and water thus simplifying the process of the prior art. The method of the present invention is generally described below where the glycerides originally present in the oil source are represented by the triglyceride, however, it is understood that the glycerides originally present in the oil source may be mono-, di-, and/or triglyicerides. Further, methanol is used as a representative alcohol, but it is understood that any alcohol may be used in this process.

Where each R may be the same or different and an aliphatic chain typically found in vegetable or animal oil sources, typically C₈ to C₂₂.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a reaction setup that may be used for performing the method of present invention.

FIG. 2 shows the acid values as a function of time for three examples of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the method of the present invention of processing a vegetable or animal oil source can be represented by the following reaction scheme where the glycerides originally present in the oil source are represented by the triglyceride, however, it is understood that the glycerides originally present in the oil source may be mono-, di-, and/or triglyicerides. Further, although methanol is used as a representative alcohol, it is understood that any alcohol may be used in this process.

Where each R may be the same or different and may be an aliphatic chain typically found in vegetable or animal oil sources, typically C₈ to C₂₂. The reaction may be typically conducted in a small-scale batch system as shown in FIG. 1 or more typically in a scaled-up version of the system shown in FIG. 1 for commercial applications. The system 8 of FIG. 1 includes a 1L resin reactor 10. The reactor 10 was equipped with a Teflon turbine agitator 12, thermocouple 14 with an associated temperature controller 16 and heating mantle 17, nitrogen sparge tube 18 with an associated nitrogen gas source 20, and a packed reflux column 22 (30 cm height and 2,5 cm diameter) attached to a Dean Stark trap 24 with condenser 26. A vacuum line 28 was attached to the top of the condenser 26 which was connected to the vacuum pump 30 via an in-line ice trap 32. The vacuum was controlled with a solenoid 34. A bubbler 36 may also be used. Those skilled in the art will also appreciate that the method of the present invention can be carried out in a continuous mode using standard equipment typically used in chemical processes.

The first step of the reaction in which the free fatty acids are converted into glycerides may be performed at a temperature between about 140° C. to about 245° C., more preferably between about 160° C. to about 200° C., and most preferably at about 180° C. The first step may further be performed at a reduced pressure ranging from about 760 mmHg to about 1 mmHg, under a constant stream of nitrogen, or a combination of both reduced pressure and under a constant stream of nitrogen.

The present invention has been found to be particularly effective when using crude glycerin derived from the methanolysis of vegetable oils or other fats (or recovered from a fat splitting process). Crude glycerin as generated from the methanolysis process contains approximately 80–85% glycerin, 13–18% methanol, about 1–2% water, small amounts of mono-, and diglycerides, as well as residual alkali. However, the method of the present invention is applicable to USP grade glycerin or purified glycerin as well. The glycerin source may be used in a concentration of at least 0.3 equivalent.

The use of crude glycerin provides an opportunity to utilize a process by-product without further purification, and enhances the rate of acid conversion in acidulated soap stock over the use of purified glycerin. This is unexpected since crude glycerin contains substantial amounts of alkaline catalyst. Therefore, a mixture containing acidulated soap stock and crude glycerin will be close to neutral in pH ca. 5.5, whereas a mixture of purified glycerin and soap stock exhibits a pH ca. 2.5–3.5. As reported in “Advanced Organic Chemistry” 4^(th) Ed., p. 395, John Wiley & Sons, N.Y., 1992, esterification reactions are acid catalyzed; thus the rate enhancement at the higher pH is unexpected.

The reaction between purified glycerin (e.g., USP grade) and soap stock proceeds (without additional catalyst) to completion (as determined by an acid value of 0.5 or less) at 220–245° C. in approximately 6 hours (see Example 9 below). At a temperature of 180° C., without added catalyst, using USP grade glycerin the esterification is complete after approximately 14 hours (see Example 1 below). A much shorter reaction time between about 9 hours and about 10 hours to completion is realized by using crude glycerin (see Examples 2 and 3 below and see FIG. 2).

The resulting mixture is then subjected to a base catalyzed alcoholysis, forming alkyl esters (e.g., methyl esters) and glycerin as a byproduct. The glycerin generated in this second step of the process can be recycled for use in the first step to form glycerides with the free fatty acids contained in acidulated soap stock or other oil source. In this latter case, no further purification of the recycled glycerin is necessary.

It is understood that any alcohol can be used in this second step of the process. It is preferred that lower molecular weight alcohols be used, such as methanol, ethanol, isopropanol, propanol and butanol. The most preferred alcohol for use in the second step is methanol. Alcohol can be provided for use in the second step of this process in an excess between about 1.0 equivalents to about 10 equivalents, more preferably in an excess between about 1.0 equivalents to about 6.0 equivalents, and most preferably in an excess between about 1.0 equivalents and about 3.0 equivalents.

The reaction scheme, in particular the first step of the reaction scheme, may be performed with a catalyst. Contemplated catalysts include but are not limited to organotin compounds (e.g., dibutyltin oxide), organo titanium compounds (e.g., tetrabutyl titanate), alkali acetates, earthalkali acetates, Lewis acids, alkali carbonates, earthalkali carbonates, and combinations thereof.

The advantages of the method of the present invention can be summarized as follows: 1) the use of the unaltered glycerin fraction obtained through alcoholysis of fats and oils; 2) rate enhancement obtained by using the unaltered glycerin fraction containing methanol, water and residual alkali from alcoholysis of fats and oils, rather than purified glycerin; 3) recyclability of glycerin fraction of the method of the invention; 4) the lower processing temperature using the unaltered glycerin fraction from alcoholysis of fats and oils; 5) reduced salt formation; and 6) eliminated setup for the separation of excess alcohol (e.g. methanol) and water.

To demonstrate the effectiveness of the above reaction scheme of the present invention, acidulated soap stock samples were subjected to the reaction scheme and the acid value of the reaction products was determined as a function of time. The decreasing acid value demonstrated that the reaction scheme provides a satisfactory method of converting the free fatty acids of the acidulated soap stock into glycerides. The first step of the reaction scheme is preferably carried out to a residual acid value of less than 5 mgKOH/g and more preferably to a residual acid value of between about 0.1 and about 1 mgKOH/g.

EXAMPLE 1

549 g of acidulated soap stock and 108 g of USP grade glycerin were charged into a 1L resin kettle 10 (FIG. 1). The reaction setup 8 of FIG. 1 was used. The resin kettle 10 was heated to the reaction temperature of 180° C. over a period of 60 minutes at atmospheric pressure. After approximately 65 minutes from the time of heat input, vacuum was applied in stages over time to reduce pressure, as reported in Table 1, to assist in the removal of reaction water. A stream of nitrogen was applied in addition to vacuum after 340 minutes of reaction time (as measured from the start of heat input). Samples were taken intermittently to monitor the reaction progress. The reaction was complete (AV=<0.5) after approximately 880 minutes. The collected distillate was measured to 26.11 g, including a thin layer on top of the reaction water, composed of light (C6–C8) fatty acids. The total recovered mass of glyceride mixture was 622.67 g.

Table 1 sets forth the reaction parameters and measured acid values of Example 1 demonstrating the progress of the conversion of the free fatty acids of the soap stock sample into glycerides.

TABLE 1 Reaction parameters for Example 1. Time Reactor Pressure ml 0.1 N AV N₂ [min] [° C.] [torr] Sample [g] NaOH [meq/g] Purge 0 22.0 760 96.60 no 10 61.0 760 no 25 121.3 760 no 50 169.7 760 no 60 180.0 760 no 65 179.5 350 no 95 179.5 350 no 105 179.4 350 1.1951 11.152 52.35 no 125 180.1 350 no 130 180.9 250 no 145 180.6 250 1.5196 11.084 40.92 no 175 179.6 250 1.3568 7.850 32.46 no 220 179.5 250 1.4444 6.050 23.50 no 280 179.8 250 1.6529 4.584 15.56 no 290 180.0 180 no 295 180.6 100 no 325 179.8 100 no 340 179.9 100 2.0267 4.056 11.23 30 mL/hr 400 180.1 100 1.6630 2.328 7.85 30 mL/hr 410 180.1 90 30 mL/hr 420 180.1 50 30 mL/hr 460 180.1 60 2.5286 2.138 4.74 30 mL/hr 640 180.0 50 2.5232 0.435 0.97 30 mL/hr 760 180.0 50 2.6908 0.250 0.52 30 mL/hr 820 180.0 50 3.0017 0.248 0.46 30 mL/hr 880 180.0 50 2.5690 0.194 0.42 30 mL/hr

EXAMPLE 2

583.9 g of acidulated soap stock and 135.97 g crude glycerin (containing 86% glycerin, and the balance as water, methanol and residual base catalyst), derived from the methanolysis of soybean oil, was charged into a 1 L resin kettle 10 (FIG. 1). The reaction setup 8 of FIG. 1 was used. The pH of the combined materials, as a 10% suspension in a 50/50 mixture by volume of isopropanol and water, was measured to 5.34. The mixture was heated to reaction temperature of 180° C. and vacuum was applied in conjunction with a nitrogen sparge to facilitate the removal of reaction water, as reported in Table 2. The total amount of distillate, including methanol and reaction water, as well as approximately 3.5 ml low molecular weight fatty acids, was measured to 58.58 g. The recovered weight of glycerides was 654.68 g (90.9% based on total mass input). In general, this example shows that by using the crude glycerin, the duration of vacuum application in combination with nitrogen sparging may be considerably shorter, and that the overall reaction time to reach a comparable acid value was significantly reduced (880 min vs. 615 min), as compared with Example 1.

Table 2 sets forth the reaction parameters and measured acid values of Example 2 demonstrating the progress of the conversion of the free fatty acids of the soap stock sample into glycerides.

TABLE 2 Reaction parameters for Example 2. Time Reactor Pressure ml 0.1 N AV N₂ [min] [° C.] [torr Sample [g] NaOH [meq/g] Purge 0 20.4 760 94.10 no 15 62.0 760 no 30 106.4 760 no 45 131.2 760 no 60 157.1 760 no 75 177.0 760 no 80 180.4 760 no 90 181.0 760 no 105 180.3 760 no 120 180.5 760 1.3349 12.848 53.99 no 135 180.7 760 no 140 180.3 350 no 150 180.4 350 1.8577 13.610 41.10 no 170 180.1 350 no 190 180.0 350 1.6703 9.378 31.50 no 195 179.7 250 no 235 179.5 250 2.3303 8.814 21.22 no 240 180.8 170 no 245 181.7 100 no 305 180.0 100 1.8723 4.284 12.84 no 365 180.5 100 2.3596 3.495 8.31 no 370 178.7 40 30 mL/hr 435 180.0 40 30 mL/hr 465 179.9 40 2.2633 1.040 2.58 30 mL/hr 615 180.1 40 2.8797 0.182 0.35 30 mL/hr

EXAMPLE 3

Example 3 demonstrates that by utilizing the combination of vacuum and nitrogen sparge earlier in the process, cycle time can be reduced further, without negatively affecting the final product, e.g., by removing raw material from the reactor resulting in decreased yields. 528.5 g of acidulated soap stock were combined with 124.4 g of crude glycerin and processed as under example 1–2. The pH of the reaction mixture immediately after combing the raw materials was measured to 5.04. The total weight of distillate was measured to 54.77 g and the isolated yield of glycerides was 589.68 g (90.3% based on total mass input).

Table 3 sets forth the reaction parameters and measured acid values of Example 3 demonstrating the progress of the conversion of the free fatty acids of the soap stock sample into glycerides.

TABLE 3 Reaction parameters for Example 3. Time Reactor Pressure ml 0.1 N AV N₂ [min] [° C.] [torr] Sample [g] NaOH [meq/g] Purge 0 20.4 760 104.20 no 15 71.4 760 no 30 111.2 760 no 35 121.0 760 no 45 140.5 760 no 60 166.0 760 no 75 180.4 760 1.6758 24.830 83.12 no 90 179.8 760 no 105 179.4 760 1.5155 17.476 64.69 no 135 180.3 760 1.1391 10.158 50.03 no 145 181.4 350 no 165 180.0 350 1.8234 12.272 37.76 no 195 180.2 350 no 200 179.5 250 no 225 179.7 250 2.0317 8.580 23.69 no 230 179.9 160 no 235 180.1 100 no 255 179.1 100 no 285 180.5 100 2.3684 5.854 13.87 30 mL/hr 290 179.9 40 30 mL/hr 345 179.8 40 2.0354 2.452 6.76 30 mL/hr 405 180.1 40 2.1778 0.802 2.07 30 mL/hr 465 179.9 40 2.3043 0.190 0.46 30 mL/hr 525 180.0 40 1.9636 0.138 0.39 30 mL/hr

FIG. 2 compares the rate of conversion of the free fatty acids of the soap stock or Examples 1, 2, and 3 and demonstrates that the conditions of Example 3 provide the most accelerated conversion.

EXAMPLE 4

Example 4 demonstrates the effect of a reduced glycerin charge. The amount of 520.2 g of acidulated soap stock and 91.8 g of crude glycerin (15 wt % effective glycerin) were charged into a 1L resin kettle 10 (FIG. 1) and treated as in the previous examples. To maintain a similar pH as in Examples 1 and 2, an adjustment was made using 7.35 g 25% solution of sodium methoxide in methanol. The total amount of distillate recovered was 53.5 g and the glyceride yield was 548.71 g.

Table 4 sets forth the reaction parameters and measured acid values of Example 4 demonstrating the progress of the conversion of the free fatty acids of the soap stock sample into glycerides.

TABLE 4 Reaction parameters for Example 4. Time Reactor Press ml 0.1 N AV N₂ [min] [° C.] [torr] Sample [g] NaOH [meq/g] Purge 0 20.4 76 104.20 no 15 72.8 76 no 25 101.5 76 no 30 112.5 76 no 35 123.2 76 no 40 133.1 76 no 50 151.5 76 no 65 173.2 76 no 75 181.2 76 no 90 180.8 76 1.2199 15.8780 73.02 no 100 179.9 76 no 105 180.2 76 no 110 181.0 76 no 120 179.5 76 1.3880 13.4200 54.24 no 130 179.2 76 no 135 179.7 55 no 140 181.3 35 no 160 178.8 35 no 165 178.4 25 no 180 180.6 25 1.3293 8.2000 34.61 no 215 179.4 25 no 240 180.4 25 1.3045 4.9940 21.48 no 245 181.6 10 no 300 179.7 10 1.2125 2.7960 12.94 no 310 180.2 4 no 360 179.9 4 1.4515 2.1060 8.14 no 370 179.7 4 30 mL/Hr 420 180.1 4 1.3065 0.5260 2.26 30 mL/Hr 570 180 4 2.0472 0.1440 0.39 30 mL/Hr

EXAMPLE 5

Example 5 is analogous to Example 4, but without the pH adjustment. The pH of the combined glycerin and soap stock was 5.03. The nitrogen sparge for the last hour was increased from 30 mL/hr to 60 mL/hr. The final amount of distillate collected was 55.25 g and 552.73 g of glycerides were recovered.

Table 5 sets forth the reaction parameters and measured acid values of Example 5 demonstrating the progress of the conversion of the free fatty acids of the soap sock sample into glycerides.

TABLE 5 Reaction parameters for Example 5. Time Reactor Press ml 0.1 N AV [min] [° C.] [torr] Sample [g] NaOH [meq/g] N₂ Purge 0 24.8 760 104.20 no 15 82.5 760 no 40 139.6 760 no 60 173.2 760 no 70 180.1 760 no 75 180.1 760 1.0755 17.1360 89.38 no 90 179.2 760 no 105 180.2 760 no 120 180.1 760 0.8893 9.4660 59.71 no 130 180.6 760 no 135 179.5 350 no 165 178.6 350 0.9661 7.4100 43.03 no 205 182.7 350 1.5781 8.9740 31.90 no 210 180.0 100 no 300 181.3 100 1.3542 4.4440 18.41 no 310 180.2 40 30 mL/Hr 420 180.0 40 1.8068 2.2180 6.89 30 mL/Hr 600 180.1 4 1.8589 0.3300 1.00 30 mL/Hr 610 180.1 5 60 mL/Hr 660 180.0 5 1.8270 0.1280 0.39 60 mL/Hr

EXAMPLE 6

Example 6 is a comparative reaction which highlights the fact that the glycerolysis can be carried out with a variety of raw material streams such as yellow grease and acidulated glycerin (recycled glycerin from soy oil methanolysis but without alkali or methanol), and can be subjected to a conventional esterification catalysis. 498.1 g yellow grease and 50.0 g acidulated glycerin were charged together with 1.0 g of Dibutyltinoxide into a 1L resin kettle 10 (FIG. 1) and heated to a reaction temperature of 200° C. When the reaction temperature reached 200° C., a vacuum of 250 mmHg was applied. After approximately 6 hours, the acid value was measured to be 0.5 AV, and about 5.5 mL liquid had been collected in the Dean-Stark trap. The reaction mixture was cooled to an appropriate temperature to safely add 116 g of methanol and 7.5 g of a 25% solution of sodium methoxide in methanol. The reactor was then heated to 77° C. for 2 hours while agitating. Heating was discontinued and the mixture was allowed to settle. A total of 147.43 g of glycerin containing phase was removed from the bottom of the mixture. The remaining material was stripped at 60° C. to remove excess methanol. The remaining crude ester phase was then washed with 110 mL of water, stirred for 5 minutes and let settle for about 30 minutes, before draining the aqueous layer from the bottom. This procedure was repeated twice more with the same amount of water. The combined aqueous phases were collected and weighed (408.2 g). The washed ester was then stripped at about 60° C. under vacuum until dry (final water content 430 ppm). The yield of biodiesel esters was 366.3 g.

EXAMPLE 7

684 g of acidulated soap stock and 163 g of crude glycerin were charged together with 3.5 g of potassium acetate (pH of mixture was 5.48) into a 1L resin kettle 10 (FIG. 1). The reaction mixture was heated to temperature and vacuum and nitrogen was applied as in the previous examples, as reported in Table 6. The final acid value was 0.21, with 72.56 g distillate collected, and a glyceride yield of approximately 758.76 g (accounting for sampling during the reaction).

After cooling the reaction, 120 g of methanol and 5.7 g of sodium methoxide solution (25% in methanol) was added, and the reactor was heated to 65–68° C. for 1.25 hours, after which the reaction mixture was allowed to settle for 1.25 hours. The glycerin fraction was then removed from the bottom of the reactor (198.33 g), followed by the removal of excess methanol in vacuo (17.66 g). The reactor was then charged with 22 g distilled water and agitated for 10 minutes. After a settling time of 3 hours, 52.57 g aqueous phase was removed (overnight an additional 10.57 g of ester was recovered from the initial aqueous phase). 254.95 g of the ester, prepared in this manner, was distilled under vacuum (10–20 mmHg) to give 224.61 g of nearly colorless methyl ester product.

Table 6 sets forth the reaction parameters and measured acid values of Example 7 demonstrating the progress of the conversion of the free fatty acids of the soap stock sample into glycerides.

TABLE 6 Reaction parameters for Example 7. Time Reactor Press ml 0.1 N AV [min] ° C. [torr] Sample [g] NaOH [meq/g] N₂ Purge 0 16.4 760 112.00 30 81.6 760 65 136.7 760 95 169.9 760 100 172.2 760 110 177.4 760 115 180.2 760 130 182.0 760 1.7476 17.350 55.70 155 180.6 760 160 180.1 400 165 180.0 350 170 182.2 250 190 180.3 250 2.0585 12.072 32.90 200 179.9 250 30 mL/Hr 230 180.4 250 30 mL/Hr 230 178.8 40 30 mL/Hr 250 181.0 40 30 mL/Hr 255 180.0 40 2.3054 6.766 16.46 30 mL/Hr 300 180.1 40 30 mL/Hr 370 179.6 40 3.2247 2.268 3.95 30 mL/Hr 435 179.6 40 4.0911 0.301 0.41 30 mL/Hr 480 179.6 40 2.7252 0.100 0.21 30 mL/Hr

EXAMPLE 8

541.29 g of acidulated soap stock and 108.5 g USP glycerin were charged together into a 1 L resin kettle 10 (FIG. 1) and heated to reaction temperature of 180° C. When the reaction temperature reached 180° C., a gradual vacuum was applied. Tetrabutyltitanate (Tyzor® TBT) was injected blow the liquid level in the reactor twice through a syringe, once at 270 min and again at 405 min elapsed reaction time. After approximately 12 hours, the acid value was measured to be 0.94 AV, and about 24.15 g distillate had been collected in the Dean-Stark trap.

Table 7 sets forth the reaction parameters and measured acid values for Example 8.

TABLE 7 Reaction parameters for Example 8. Time Reactor Pressure ml 0.1 N AV N₂ [min] [° C.] [torr] Sample [g] NaOH [meq/g] Purge 0 33 760 96.60 no 15 77.6 760 no 30 128.6 760 no 45 160.6 760 no 60 177.5 760 1.7029 25.616 84.39 no 65 180.3 500 no 70 181.7 450 no 90 180.5 450 1.1478 13.330 65.15 no 120 180.0 450 1.4322 12.616 49.42 no 150 180.1 450 no 165 180.3 450 no 180 179.5 450 1.5293 8.768 32.16 no 185 180.5 370 no 188 181.1 350 no 270 180.1 350 1.7471 5.120 16.44 no 285 180.0 350 no 300 180.5 350 no 302 180.5 290 no 305 181.1 250 no 330 180.5 250 1.5455 3.466 12.58 no 345 178.8 150 30 mL/Hr 360 180.7 100 30 mL/Hr 390 180.1 100 1.9501 3.036 8.73 30 mL/Hr 405 180.1 60 no 420 180.1 60 no 450 179.4 60 2.1709 2.274 5.88 no 510 179.7 50 1.4046 0.944 3.77 no 690 180.1 40 2.6843 0.885 1.85 no 710 179.6 15 30 mL/Hr 740 179.9 15 2.4716 0.416 0.94 30 mL/Hr

EXAMPLE 9

250.7 g yellow grease (AV 29.5 mgKOH/g) was charged together with 14.7 g of acidulated glycerin and heated to a reaction temperature of 230° C. After 45 minutes into the reaction, a vacuum was applied at 23 inches to facilitate removal of water. After 8 hours reaction time the acid value was 0.37.

EXAMPLE 10

515.0 g acidulated soap stock (acid value 126 mgKOH/g) were charged together with 133.1 g of acidulated glycerin and heated to 230° C. After 45 minutes at 230° C. vacuum was applied at 20 inches to assist in the removal of reaction water. After a total reaction time of 7.5 hours, the acid value was 0.34.

Table 8 summarizes the reaction parameters and AV results for Examples 1 through 10.

TABLE 8 Summary of results for Examples 1–10. Reaction Rxn Wt % Final Time Temp. Example Glycerin AV [min] [° C.] Added Catalyst 1   20 (P) 0.42 880 180 None 2   20 (C) 0.35 615 180 None 3   20 (C) 0.39 525 180 None 4   15 (C) 0.39 570 180 None 5   15 (C) 0.39 660 180 None  6*   10 (R) 0.50 360 200 0.5 wt % DBTO 7   20 (C) 0.41 435 180 0.5 wt % KAc 8   20 (P) 0.94 740 180 0.2 wt % TBT  9* 5.75 (R) 0.37 480 230 None 10    25 (R) 0.34 450 230 None n.d. = not determined *= Reaction run with yellow grease (12 wt % Free fatty acid) as comparison DBTO = Dibutyl tinoxide TBT = Tetrabutyltitanate Crude glycerin ca. 86% pure (C) USP glycerin >99.9% pure (P) Glycerin recycled ca. 98% pure (R)

EXAMPLE 11

Example 11 demonstrates the effectiveness of the method of the present invention on a large scale. To 1,670 lbs of acidulated soap stock, 304 lbs of glycerol were added. The mixture was agitated and heated to 180° C. reaction temperature, while removing residual methanol from the recycled glycerin as well as reaction water from the formation of glycerides. The removal of reaction water was facilitated by the use of vacuum (40 mmHg max.) and nitrogen sparging. After approximately 16 hours (including approximately 2 hours heat up time), an acid value of 1.0 was reached. The reaction was cooled to <60° C. and methanol was charged (732 lbs) as well as 45 lbs of sodium methylate (21% solution in methanol). The reactor was heated to 68° C. and maintained at this temperature for one hour. Agitation was then stopped and the glycerol phase was allowed to settle at the bottom of the reactor for approximately 1 hour. After draining the glycerol phase, residual methanol was removed via vacuum, and 20 lbs of wash water were added and the mixture was stirred for 15 min and then left to settle. The aqueous phase was removed from the bottom of the reactor. The reactor was then evacuated to remove residual water resulting in a crude methyl ester product. The crude methyl ester was then subjected to vacuum distillation yielding approximately 1,429 lbs of nearly colorless distilled ester.

EXAMPLE 12

Example 12 demonstrates the effectiveness of the method of the present invention on a large scale. To 1,521 lbs of acidulated soap stock, 380 lbs of glycerol were added, consisting of 304 lbs crude glycerol from the methanolysis of soybean oil and 76 lbs of the recycled glycerin fraction of the previous large scale run of Example 10. The mixture was agitated and heated to 180° C. reaction temperature, while removing residual methanol from the recycled glycerin as well as reaction water from the formation of glycerides. The removal of reaction water was facilitated by the use of vacuum (40 mmHg max.) and nitrogen sparging. After approximately 12 hours (including approximately 2 hours heat up time), an acid value of 0.5 was reached. The reaction was cooled to <60° C. and methanol was charged (434 lbs) as well as 41 lbs of sodium methylate (21% solution in methanol). The reactor was heated to 68° C. and maintained at this temperature for one hour. Agitation was then stopped and the glycerol phase was allowed to settle at the bottom of the reactor for approximately 1 hour. After draining the glycerol phase residual methanol was removed via vacuum, and 20 lbs of wash water were added and the mixture was stirred for 15 minutes and then left to settle. The aqueous phase was removed from the bottom of the reactor. The reactor was then evacuated to remove residual water resulting in a crude methyl ester product. The crude methyl ester was then subjected to vacuum distillation yielding approximately 1,370 lbs of nearly colorless distilled ester.

While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. Therefore, it is understood that the embodiments described above are merely for illustrative purposes and are not intended to limit the spirit and scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents. 

1. A method of making an alkyl ester comprising the following steps: providing an oil source, the oil source including free fatty acids or glycerides; providing a glycerol source of at least 0.3 equivalents; contacting the glycerol source and the oil source for a sufficient time for effective conversion of the free fatty acids and the glycerides into a mixture of mono-, di-, and tri-glycerides; providing an alcohol in an excess between about 1.0 equivalents to about 10 equivalents; reacting the mixture of glycerides with the alcohol for an effective conversion of the glycerides into fatty acid alkyl esters; and recovering the fatty acid alkyl esters.
 2. The method of claim 1, wherein the alcohol is selected from the group consisting of methanol, ethanol, isopropanol, propanol, and butanol.
 3. The method of claim 1, wherein the alcohol is provided in an excess between about 1.0 equivalents to about 6.0 equivalents.
 4. The method of claim 1, wherein the alcohol is provided in an excess between about 1.0 equivalents to about 3.0 equivalents.
 5. The method of claim 1, wherein a vacuum is applied to reduce pressure over time during the step of contacting the glycerol source and the oil source.
 6. The method of claim 5, wherein the pressure is maintained at about 760 mmHg while heat is applied during the contacting step to reach reaction temperature, and the pressure is reduced over time after the reaction temperature has been reached.
 7. The method of claim 5, wherein the pressure is reduced over time from about 760 mmHg to less than about 100 mmHg.
 8. The method of claim 6, wherein the pressure is reduced over time from about 760 mmHg to less than about 100 mmHg.
 9. The method of claim 6, wherein the pressure is reduced over time from about 760 mmHg to between about 30 mmHg and about 60 mmHg.
 10. The method of claim 6, wherein the pressure is reduced over time from about 760 mmHg to less than about 30 mmHg.
 11. The method of claim 6, wherein the pressure is reduced over time from about 760 mmHg to less than about 10 mmHg.
 12. The method of claim 5, wherein the pressure is reduced over time and a constant stream of nitrogen is applied during the step of contacting the glycerol source and the oil source.
 13. The method of claim 12, wherein the constant stream of nitrogen is not applied until the pressure has been reduced to about 100 mmHg.
 14. The method of claim 12, wherein the constant stream of nitrogen is not applied until the pressure has been reduced to less than about 100 mmHg. 